To find the product of the two complex numbers \(5i\) and \(4i\), we can multiply them together:
\[ 5i \times 4i = 20i^2 \]
Since \(i^2 = -1\), we have:
\[ 20i^2 = 20(-1) = -20 \]
Thus, the product of \(5i\) and \(4i\) is \(-20\).
Looking at the options provided:
- \(9i\) (not equivalent)
- \(4i \times 5i\) (this is the original expression, not a numerical answer)
- \(20i\) (not equivalent)
- \(20\) (not equivalent to \(-20\))
None of the options precisely match the correct answer, \(-20\). However, if the correct answer is looking for a numerical expression without signs, the answer could be interpreted differently, but in strict terms, the equivalent of \(5i \times 4i\) is indeed \(-20\), and none of the options provided are equivalent to that value.